The overall objective is to study proteins from biological membranes, so as to gain an understanding of the unique type of physiological function that is mediated by these proteins. The methodology required to bring membrane proteins into solution, where they can be purified and investigated by the traditional methods of protein chemistry, has been developed in previous years. We are now studying two proteins in detail. One is the Ca ion-activated ATPase from sarcoplasmic reticulum, which is involved in regulation of muscle function. It is an example of an ion pump, mediating active transport of Ca ions. The other protein is rhodopsin from vertebrate visual receptor cells. It is an example of a primary sensory receptor, and the mechanism by which it works may involve light-induced formation of an ion channel through the membrane of the disks in the outer segments of the receptor cell. In both cases we are combining structural studies with functional studies, so as to arrive eventually at a mechanism at the molecular level.